Reference is made to copending parent application Ser. No. 08/991,145 filed on Dec. 16, 1997, the subject matter of which is incorporated herein by this reference thereto.
Lysine is an amino acid used extensively in the animal feed industry, the major form of which is L-LysineHCl (L-Lysine monohydrochloride). For many years, an L-LysineHCl solid has been produced by a process of fermentation, purification, crystallization and drying. After fermentation, the resulting broth may be rendered cell free by filtration or centrifugation. After filtration, the L-Lysine may be recovered from the fermentation broth by an ion exchange step, that produces a liquid which is substantially L-Lysine free base. This solution may then be concentrated by evaporation.
Hydrochloric acid was usually added to the concentrated L-Lysine free base to form L-LysineHCl. This concentrated L-LysineHCl solution was crystallized to produce a product in the form of L-LysineHCl dihydrate (L-LysineHCl:2H.sub.2 O). This crystallized solid was thereafter dried to have less than one percent moisture.
This conventional product may have shortcomings. For example, it is dusty. During the handling of the product, the dust results in a loss of valuable material and sometimes causes an incomplete formulation. Also, human working conditions are made less healthful and more difficult as a result of the dust contributed by the L-LysineHCl. Sometimes the product develops lumps during storage which are difficult to break up at the time of end use. In addition, the extensive use of an ion exchange makes this process expensive.
Direct spray drying of an L-Lysine fermentation broth avoids the extensive purification steps associated with the L-Lysine hydrochloride process, in particular the use of an expensive ion-exchange. However, consistent L-Lysine concentration in the final dry product is difficult to achieve because the L-Lysine concentration in a fermentation broth can vary considerably. Also, the dry product may be dusty and difficult to use.
U.S. Pat. No. 5,431,933 describes a process for the production of an amino acid feed supplement which "still contains most of the solids content of the fermentation broth." The production of a fermentation broth at the industrial scale with 40 to 50 percent L-Lysine content is very difficult to achieve from an operational standpoint. Malfunctioning fermenters, contamination, power outages, and operator error are quite common and are likely to lead to fermentation material that is less than about 40 percent L-Lysine and therefore of little value. This difficulty is compounded by the impurities associated with the media components, many of which are unrefined and vary in solids content and nutrient value from lot to lot. To avoid variance in media, fermentation is constrained to specific and expensive media. These considerations may lead to an increase in operational input which is necessary to make a 40 to 50 percent L-Lysine product, leading to high manufacturing costs which may be prohibitive.
A process in which a non-dusty granular animal feed product is formed is described in U.S. Pat. No. 5,622,710. First, the fermentation broth is spray dried to produce particles which may include biomass. In the second step, the particles are converted into pellets by means of costly high shear mixing equipment.
European Application Number 91460051.5 describes a method of making a granulated L-Lysine dust free, free-flowing, L-LysineHCl granular product from a liquid solution or slurry by a spray granulation process. In one embodiment of the invention, elements from a fermentation broth containing L-Lysine is ion exchanged to produce a purer L-Lysine solution. Hydrochloric acid is then added to the purer L-Lysine solution to make L-LysineHCl which is then sprayed onto an agitated drying bed of L-Lysine particulates. The particles of L-LysineHCl are then recovered once they reach a predetermined size.
International Publication Number WO/95/23129 describes the production of non-stoichiometric salt of L-Lysine in granular form. This publication teaches the production of non-stoichiometric salts of L-Lysine wherein the amount of L-Lysine content in the final product is adjustable. While the requirement for hydrochloric acid is reduced, other materials are called for such as calcium hydroxide, sulfuric acid or phosphoric acid. In addition, the fermentation broth containing the L-Lysine is extensively ion-exchanged.
U.S. Pat. No. 3,089,824 describes the use of a fluidized bed for the manufacture of compressed tablets for medical use. The process comprises (1) forming a suspension of particles in air, (2) enabling the particles to be built up with granulating material, and (3) coating the resulting granules with a lubricant. In one aspect of this invention, the granulating material is atomized and sprayed into the air stream of a fluidized bed of inert particles such as sucrose. The inert particles act as nuclei for the granulation process. The resulting granules are coated with a lubricant.
The copending parent application (Ser. No. 08/991,145 filed on Dec. 16, 1997) describes an extremely useful process for making a substantially non-dusty granular L-Lysine product in which the concentration of L-Lysine in the final product is controlled by the addition of material containing L-Lysine, which is added prior to an agglomeration step (i.e. spray granulation step). There are occasions where a non-granular L-Lysine feed supplement with an adjustable amount of L-Lysine purity is desirable on economic grounds.
As useful as the copending parent application is, the process describes an ultrafiltration step to provide a substantially cell free L-Lysine broth and a cell rich L-Lysine broth in the form of a permeate and a retentate respectively. The cell rich L-Lysine broth is abandoned as waste. The ultrafiltration step adds considerably to plant costs.
Care should be taken either to use or to properly dispose of the cell rich L-Lysine broth. The cell rich L-Lysine broth is frequently treated as a waste by-product and requires primary and secondary waste water treatments. If the cell rich L-Lysine broth is released as untreated sewage this may have a deleterious impact on the environment.